Ecological Baseline Studies Report Proposed Dry Lake Wind Project, Navajo County, Arizona


Title: Ecological Baseline Studies Report Proposed Dry Lake Wind Project, Navajo County, Arizona
Publication Date:
June 20, 2007
Pages: 63

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Young, D. Jr.; Poulton, V.; Bay, K. (2007). Ecological Baseline Studies Report Proposed Dry Lake Wind Project, Navajo County, Arizona. Report by Western Ecosystems Technology Inc (WEST). pp 63.

PPM Energy, Inc. (PPM) is proposing to construct, operate, and maintain a wind generation facility in Navajo County, Arizona. PPM's project, the Dry Lake Wind Power Project , is located about 6 to 18 miles north-northwest of the City of Snowflake, just east of Arizona State Highway 377 and southwest of the I-40 corridor. The Project would provide up to 378 megawatts (MW) of wind-generated energy and consist of multiple phases:


  • Phase I would include 64 MW of wind energy with up to 43 wind turbines, access roads, an interconnection substation, an Operations & Maintenance (O&M) facility, and collector lines to transmit the generated energy to the substation. The turbines would range in size from 1.5 to 3.0 MW each.
  • Subsequent phases would include comparable facilities with capacity to provide a total of up to 314 MW of additional wind energy.


The turbines, access roads, collector lines, substation and O&M facilities would be constructed on private leased land, Arizona state lands, and federal lands managed by the Bureau of Land Management.


As part of the environmental impact evaluation for the project, a detailed 12-month baseline ecological resources study plan was developed and implemented at the site. The study protocol was developed in cooperation with the Arizona Game and Fish Department and the U.S. Fish and Wildlife Service and based largely on previous studies of wind power effects on wildlife. Objectives of the study were to provide data that are useful in evaluating potential impacts from the proposed project and to assist in siting of project facilities within the project area. The field surveys were designed to: (1) describe and quantify seasonal avian use of the proposed project area; (2) describe and quantify raptor use and nesting in the proposed project area; (3) investigate the presence and relative abundance of bats on the proposed project area; and (4) describe vegetation types and rare plant occurrence in the proposed project area. This report includes results of studies on all phases of the project. The Phase I area was studied in greater detail to cover the areas that would be developed first. It is the intent to expand these studies once the layout and scope of subsequent phases are finalized.


Fixed-point avian use surveys were conducted to estimate the seasonal, spatial, and temporal use of the site by birds and in particular raptors. Surveys were conducted at half (5-6) of the 11 fixed-point count stations located within the study area approximately once each week between September 12, 2005 and September 15, 2006, resulting in 279 30-minute point count surveys during the study. Sixty-five avian species were observed during the surveys. Passerines were the most numerous group and comprised over 95% of all birds observed. Horned lark, common raven, mountain bluebird, and dark-eyed junco were the most abundant passerines. Raptors comprised only 1% of all birds observed. The most common raptor was red-tailed hawk. Other birds (shorebirds, doves, non-passerines) comprised approximately 3% of all birds observed.


To standardize the data for comparison between points, seasons, and with other studies, avian use, frequency of occurrence, and species composition were calculated from observations within 800 m of the survey point. Avian use by species was calculated as the mean number of observations per 30-minute survey. Over all seasons based on us e, passerines were the most abundant group (19.44/survey), followed by doves (0.44/survey) and raptors (0.22/survey). Horned lark was the most common bird observe d with 12.76 detections per survey, followed by common raven (1.90), mountain bluebird (0.62), and dark-eyed junco (0.57). These four species comprised 78% of all bird us e of the site for the year.


During the point count surveys 782 groups totaling 4273 individual birds were observed flying. For all species combined, 90.2% of all birds observed flying were below, 8.1% were within, and 1.8% of birds were above the turbine rotor-swept height. For species with at least five observations of flying birds, those most often observed at rotor-swept heights were Townsend's solitaire (71.4%), golden eagle (60.0%), turkey vulture (50.0%), common raven (44.4%), and red-tailed hawk (42.9%). Based on the use (measure of abundance) of the site by each species and the flight characteristics observed for that species, common raven, pinyon jay, horned lark, and Townsend's solitaire had the highest probability of turbine exposure. The only raptor with a relatively high exposure index was red-tailed hawk, which ranked 8th of all species. Mean use and raptor flight paths were plotted by survey point. Based on that analysis, raptor use was concentrated along the slopes of Pink Cliffs in the southern portion of the study area.


An aerial survey for raptor nests was conducted via helicopter on May 23, 2006 and via ground surveys on May 4, 2007. The aerial nest survey area included the area within an approximate 2-mile buffer of the Phase 1 site. The total area searched was approximately 45,787 acres (71.5 mi2). Four active raptor nests were located during the survey: one golden eagle nest, a red-tailed hawk nest, a great horned owl nest, and a barn owl nest. The only nest within the Phase 1 project area boundary was a barn owl located in a cave within the Pink Cliffs area. The golden eagle nest was located approximately 0.75 mile southeast of the project area. A pair of adult golden eagles was observed on a power line tower but no nest was observed at that location. The red-tailed hawk nest was located approximately 0.3 miles south of the project area, and the great horned owl nest was located approximately 1.0 mile west of the project area. Based on the total survey area, active raptor nest density was 0.05/mi2, which is low compared to most other wind resource areas in the western U.S. Two common raven nests and no raptor nests were located in the subsequent phases area, however, the study area contained some habitat features such as large bluffs (mesas) and canyons which could not thoroughly be covered by ground based surveys.


The objective of the bat use surveys was to estimate the relative abundance and spatial use of the site by bats and determine species of bats using the project area, to the extent possible. AnaBat detectors were deployed at two sampling stations using passive sampling methods. One location was at the project met tower in the southeast portion of the project. The other location was based on habitat and was near a complex of ground fissure s or caves that could support roosting bats. A third area near a stockpond was sampled for three nights in July when the AnaBats were first deployed. AnaBat detectors were operated from July to November, however due to technical difficulties sampling did not occur over this whole period.


The number of bats detected per detector night varied from 3.0 in July to 0 in November. Over all sampling nights, 1.78 bats per detector night were recoded with greatest use at the sampling station adjacent to the ground caves. While bat call characteristics overlap among species, several species of bats were recorded on site or presumed present based on the characteristics of call and other regional research in similar habitat including pallid bat, Brazilian free-tailed bat, fringed myotis, yuma myotis, California myotis, and western pipistrelle.


Background information indicated that three sensitive plant taxa may potentially occur in the proposed project area: roundleaf er razurizia, paper-spined cactus, and Peebles Navajo cactus. The survey for sensitive plant species was conducted from April 24-27, 2006 and involved meandering pedestrian transects across the project site at proposed turbine locations and along proposed project roads. A 150-meter buffer was surveyed around turbine locations and an approximately 10-meter buffer was surveyed along either side of existing access roads. No individuals of roundleaf errazurizia or Peebles Navajo cactus were found within the project site. A total of nine subpopulations of paper-spined cactus were detected within the project site. The number of individuals within each of the subpopulations ranged from 6 to 35 individuals.


The Phase 1 project area was also surveyed for wetlands and other waters of the U.S. during the rare plant survey. The survey area included a 150-meter buffer on all turbine locations and an approximately 10-meter buffer along either side of existing access roads. No wetlands were identified within the Phase 1 project boundary. Three waterbodies meeting the criteria for waters of the U.S. were mapped on site, including Washboard Wash, a tributary to Washboard Wash, and an unnamed tributary.


Based on the use data collected for the Dry Lake site, mean annual raptor use (adjusted as number of raptors observed per 20- min survey within an 800-m radius for comparison with other wind project studies) was 0.15/survey. Raptor use at Dry Lake is lower than most wind resource areas evaluated in the U.S. using similar protocols. A regression analysis of raptor use and raptor mortality for several newer wind projects where similar methods were used to obtain raptor use estimates showed a significant (r2 = 90.3%) correlation between raptor use and collision mortality. Using this regression to predict raptor mortality at the Dry Lake project yielded an estimated fatality rate of 0.0/MW/year, or no raptors per year for a 100-MW project. A 90% confidence interval around this estimate is 0 to 0.10 raptor fatalities/ MW/year, or 0 to 10 raptor fatalities per year for a 100-MW project. Based on species composition of the most common raptor fatalities at other western wind farms and species composition of raptors observed at Dry Lake during the fixed-point surveys, the majority of the fatalities of diurnal raptors would likely consist of red-tailed hawks and American kestrels. Small numbers of other raptors may occur as fatalities over the life of the project.


Mean use data expressed as the number of birds observed per 20-minutes with an 800-m viewshed are available for 25 other wind resource areas (WRAs) in the U.S. Use of the Dry Lake site by all bird species combined is moderately high compared to these WRAs, and is higher than 18 of the other sites. However, the vast majority of the Dry Lake use is due to horned larks, a species common in flat desert scrub and grazed rangeland. The data collected during this study suggest that the Dry Lake project is not within a major migratory pathway or does not provide important stopover habitat for migrants as there was generally low variation in avian diversity across seasons. Based on all survey data, passerine mortality at Dry Lake would likely be similar to the national average of 3.1 birds/MW/year. Because habitat at the Dry Lake site is not unique for the area, and similar habitats are common in the region, it is unlikely that displacement of birds would result in any substantial imp acts or population changes.


The number of bats recorded per AnaBat detector night was most similar to other western wind projects studied. The number of bats recorded does not suggest that bat mortality would be high; however, Brazilian free-tailed bats, documented fatalities at other wind projects, were likely present on the site based on the bat calls recorded. Other species that are expected fatalities would include long distance migrant species such as hoary bat and silver-haired bat although habitat for these species does not occur on the site. These species are common fatalities at all wind projects studied in the U.S. Typical resident bats or species that make short distant dispersals from suitable hibernacula are not expected to be greatly affected by the project. Bat use of the subsequent phases area is expected to be similar to the Phase 1 study area but may be more consistent if perennial water sources are expected.

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